A power generator installed in a vehicle is coupled to a crankshaft of an engine via an auxiliary drive belt. When a driver removes his/her foot from an accelerator pedal as the vehicle travels, a fuel supply to the engine is stopped. Accordingly, the vehicle decelerates. Rotation of tires is transmitted to the engine via a drive train, and then transmitted to the power generator via the belt. As a result, the power generator generates power. Thus, kinetic energy that would otherwise be discarded is collected as electric energy. This type of power generation is known as regenerative power generation. With regenerative power generation, power can be generated without consuming fuel, and therefore a fuel efficiency of the vehicle improves.
However, the power generator is coupled to the crankshaft of the engine via the auxiliary drive belt, and therefore a part of an engine output generated in response to depression of the accelerator pedal by the driver is consumed by the power generator. As a result, an acceleration performance of the vehicle deteriorates.
Hence, in JP2007-170238A, a power generation capacity of the power generator is varied in accordance with a travel condition of the vehicle. When the vehicle accelerates, the power generation capacity of the power generator is suppressed by suppressing or stopping an operation of an auxiliary machine. In so doing, a torque for driving the power generator is suppressed, and therefore the acceleration performance of the vehicle does not deteriorate.